Effect of Sand Content on the Workability and Mechanical Properties of Concrete Using Bottom Ash and Dredged Soil-based Artificial Lightweight Aggregates

Kyung-Ho Lee,Ju-Hyun Mun,Keun-Hyeok Yang,Nguyen Van Tuan

doi:10.1186/s40069-018-0306-z

Abstract

The objective of this study is to examine the workability and various mechanical properties of concrete using artificial lightweight aggregates produced from expanded bottom ash and dredged soil. Fifteen concrete mixes were classified into three groups with regard to the designed compressive strengths corresponding to 18 MPa, 24 MPa, and 35 MPa. In each group, lightweight fine aggregates were replaced by using natural sand from 0 to 100% at an interval of 25%. Thus, the density of concrete ranged between 1455 and 1860 kg/m3. Based on the regression analysis using test data, a reliable model was proposed to clarify lower early-age strength and higher long-term strength gains of lightweight aggregate concrete (LWAC) when compared with the predictions of the fib model. The proposed model also indicates that a lower water-to-cement ratio is required with the decrease in the natural sand content to achieve the designed compressive strength of concrete. The partial use natural sand is favorable for enhancing the tensile resistance capacity, shear friction strength, and bond behavior with a reinforcing bar of LWAC. The fib model overestimates direct tensile strength, bond strength and the amount of slip at the peak bond stress of LWAC. Therefore, it is necessary to consider the density of concrete as a critical factor in conjunction with its compressive strength to rationally evaluate the various mechanical properties of LWAC.

Highlights

Lightweight aggregates have been artificially produced by the thermal treatment of industrial by-products or waste materials such as fly ash, bottom ash, palm oil fuel ash, and dredged soil (Aslam et al 2016; Jo et al 2007; Lotfy et al 2015; Yang et al 2011)
The long-term strength gain ratios are higher when compared with the conventional values of 1.05–1.2 determined from normal-weight concrete (NWC) (ACI Committee 318)
This study examined the effect of natural sand content and water-to-cement ratio on the mechanical properties of lightweight aggregate concrete using expanded bottom ash and dredged soil granules (LWAC-BS)

Summary

Introduction

Lightweight aggregates have been artificially produced by the thermal treatment of industrial by-products or waste materials such as fly ash, bottom ash, palm oil fuel ash, and dredged soil (Aslam et al 2016; Jo et al 2007; Lotfy et al 2015; Yang et al 2011). It is commonly known that these types of recycled artificial lightweight aggregates are structurally strong, physically stable, durable, and environmentally favorable (Jo et al 2007). The lightweight aggregates typically possess higher water absorption and lower density when compared with those of the conventional normal-weight aggregates. High water absorption by the aggregates leads to rapid slump loss and shorter setting time of fresh concrete when the aggregates are not pre-controlled by moist treatment prior to mixing (Yang et al 2014). Aggregate particles with a lower density when compared with that of the surrounding cementitious matrix may cause segregation since they flow to the upper surface of the concrete. Artificial lightweight aggregates frequently exhibit discontinuous particle distribution and especially in the case of fine aggregates due to the difficulty of producing a particle size less than 1.25–2.5 mm. The discontinuous grading of the aggregate particles reduces the tensile resistance capacity of concrete that leads to the development of unexpected cracks in concrete members

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Results

Conclusion